Method and apparatus for separating particles by size

Abstract

A method and apparatus for separating a mixture of particles of various sizes in a capillary tube into groups by size using multiple forces of controlled amplitude. Ultrasonic radiation at a first selected frequency is applied to set up a standing pressure wave in the capillary tube, resulting in a first aggregating force which causes particles of all sizes to aggregate at positions within the capillary tube which correspond to nodes or anti-nodes of the standing wave. Transverse vibrations are also applied to the capillary tube. The frequency of the ultrasonic radiation is adjusted to reduce the magnitude of the first aggregating force. Inertial forces resulting from the transverse vibrations then cause the particles to separate by size. The apparatus and method allows a mixture of particles to be separated by size quickly, without requiring the use of high voltages.

1. An apparatus for separating by size particles suspended in an acoustic medium, comprising:
 (a) a vessel; 
 (b) an acoustic medium in the vessel; and 
 (c) at least one ultrasound transducer for applying a longitudinal acoustic field in a first direction to the acoustic medium in the vessel to aggregate the particles in the medium and a second acoustic field in a second direction to separate the particles by size, wherein the second direction is transverse to the longitudinal direction. 
 
   
   
     2. The apparatus of  claim 1  wherein at least a portion of the vessel is curved around at least a portion of at least one ultrasound transducer. 
   
   
     3. The apparatus of  claim 1  wherein at least a portion of the vessel is formed in a loop around at least a portion of at least one ultrasound transducer. 
   
   
     4. The apparatus of  claim 1  wherein the at least one ultrasound transducer comprises a single ultrasound transducer for applying both the first acoustic field and the second acoustic field to the acoustic medium in the vessel. 
   
   
     5. The apparatus of  claim 1  wherein the at least one ultrasound transducer comprises a first ultrasound transducer for applying the first acoustic field and a second ultrasound transducer for applying the second acoustic field. 
   
   
     6. The apparatus of  claim 1  wherein the vessel comprises a glass capillary tube. 
   
   
     7. The apparatus of  claim 6  wherein at least a portion of the vessel is curved around at least a portion of at least one ultrasound transducer. 
   
   
     8. The apparatus of  claim 6  wherein the vessel is formed in a loop around at least a portion of at least one ultrasound transducer. 
   
   
     9. The apparatus of  claim 6  wherein the at least one ultrasound transducer comprises a single ultrasound transducer for applying both the first acoustic field and the second acoustic field to the acoustic medium in the vessel. 
   
   
     10. The apparatus of  claim 6  wherein the first acoustic field creates a standing pressure wave in at least a portion of the vessel. 
   
   
     11. A method of separating by size a mixture of particles of various sizes comprising:
 (a) suspending the mixture of particles of various sizes in an acoustic medium in a tube; 
 (b) applying a first acoustic radiation in a longitudinal direction in the tube to create a standing pressure wave in at least a portion of the acoustic medium thereby forming an aggregate of the mixture of particles of various sizes near a node of the standing pressure wave; and 
 (c) applying a second acoustic radiation in a transverse direction in the tube to separate the particles by size 
 whereby the aggregate of the mixture of particles of various sizes is separated by size. 
 
   
   
     12. The method of  claim 11  wherein at least a portion of the tube is curved. 
   
   
     13. The method of  claim 11  wherein at least a portion of the tube is formed in a loop. 
   
   
     14. The method of  claim 11  wherein a piezoelectric plate is used to apply at least a portion of the first acoustic radiation. 
   
   
     15. The method of  claim 11  further comprising the step of increasing the intensity of the first acoustic radiation. 
   
   
     16. The method of  claim 11  further comprising the step of increasing the frequency of the first acoustic radiation. 
   
   
     17. The method of  claim 11  further comprising the step of decreasing the intensity of the first acoustic radiation. 
   
   
     18. The method of  claim 11  further comprising the step of decreasing the frequency of the first acoustic radiation. 
   
   
     19. The method of  claim 11  wherein the tube comprises a glass capillary tube. 
   
   
     20. The method of  claim 19  wherein at least a portion of the tube is curved. 
   
   
     21. The method of  claim 19  wherein at least a portion of the tube is formed in a loop. 
   
   
     22. The method of  claim 19  wherein a piezoelectric plate is used to apply at least a portion of the first acoustic radiation. 
   
   
     23. The method of  claim 19  further comprising the step of increasing the intensity of the first acoustic radiation. 
   
   
     24. The method of  claim 19  further comprising the step of increasing the frequency of the first acoustic radiation. 
   
   
     25. The method of  claim 19  further comprising the step of decreasing the intensity of the first acoustic radiation. 
   
   
     26. The method of  claim 19  further comprising the step of decreasing the frequency of the first acoustic radiation.